This invention relates in general to dynamoelectric machines and, more particularly, to apparatus for connecting stator lamination sectors to the stator frame of such machines.
FIG. 1 shows a cross section of a simplified conventional dynamoelectric generator 10. Generator 10 includes a stator 12 which exhibits a generally annular shape. The outermost portion of generator 10 and stator 12 is the generator frame 13.
A stator core 14 is built up by stacking a large quantity of stator lamination sectors 16 together in sandwich-like relationship. Stator lamination sectors 16 are attached to the stator in a manner described in more detail later in this background.
A rotor 20 is rotatably mounted in a cylindrical opening 22 formed along the central axis 24 of stator 12. That is, rotor 20 is coaxially positioned within stator 12 such that rotor 20 may be freely turned with respect to stator 12. Rotor 20 and stator 12 include respective windings (not shown). External excitation power is generally supplied to the rotor field windings via slip rings (not shown) coupled to an external power source. Thus, when mechanical energy is applied to rotor 20 to cause rotor 20 to spin on its axis 24, a moving magnetic field is generated which rotates at the same rate as rotor 20. This moving magnetic field cuts across the stator windings thus causing an electric current to be generated with the stator field windings.
As background for understanding the improved structure of the present invention which mechanically couples stator core lamination sectors to the stator frame, it is helpful to understand one conventional structure for accomplishing this task. One such apparatus for attaching stator lamination sectors to a stator frame is described and claimed in U.S. Pat. No. 4,564,779, entitled "Dynamoelectric Machine Stator Using Cylindrical Keybars", issued to Terry, Jr. and assigned to the same assignee as the present invention. The disclosure of U.S. Pat. No. 4,564,779 is incorporated herein by reference.
FIG. 2 discloses a stator 30 which includes a generally annular stator frame 40, formed by outer wrapper 42 and a plurality of web plates 44 arranged in annular fashion as indicated in the portion of stator 30 shown in perspective. Keybars 50 include opposed ends, one of which is shown as 50A. A plurality of keybars 50 are situated in respective holes 52 which are machined in the radially inner edge 56 of web plates 44. Keybars 50 are used to. attach lamination sectors 58 to web plates 44 as described subsequently. As seen in FIG. 2 and more clearly in the cross section of a portion of stator 30 in FIG. 3, holes 52 are bored sufficiently close to the radially inner edge 56 such that the perimeters of cylindrical bore holes 52 exhibit broken portions 59 at inner edge 56 thereof. Returning to FIG. 2, keybars 50 are oriented parallel with the central axis 57 of stator 30 and extend within holes 52 essentially from one end of stator 30 to the other. Although only a portion of a stator web plate 44 including two holes 52 is shown in FIG. 2, a complete stator 30 includes holes 52 which are equally chordally spaced around the entire radially inner edge 56 of web plates 44.
As seen in FIGS. 2 and 3, keybars 50 each have a cylindrical portion 60 which is situated within holes 52 and a dovetail portion 62 which extends radially inward from cylindrical portion 60. The dovetail portions 62 of keybars 52 mate with respective dovetail slots 64 in the radially outer curved edge 66 of stator core lamination sectors 58. That is, as seen in FIG. 3, sectors 58 actually hang from the dovetail portions 62 by the dovetail slots 64 of sectors 58 which are mated in dovetail portions 62.
For completeness of description, the portion of stator 30 shown in FIGS. 2 and 3 includes one of a plurality of stator slots 70 which contain conventional current carrying conductors 72. Stator conductors 72 are held in slots 70 by a conventional dovetail retaining bar 74.
Although only a portion of one stator core lamination sector 58 is shown in FIGS. 2 and 3, the stator core is actually built up by stacking large numbers of such sectors 58 side by side each other in sandwich-like relationship along the dovetails 62 of keybars 50. Generally, sectors 58 are segmental insulated laminations of silicon steel, each typically on the order of 10 to 20 mils thick. A close-up end view of the lower portion of one of keybars 50 is shown in FIG. 4 to illustrate in detail the dovetail portion 62 along which lamination sectors 58 are stacked.
FIG. 5A is a complete front view of one of the stator lamination sectors 58 which are stacked on keybars 50 to form the stator core. In this particular example, sector 58 includes three dovetail slots 64 (also referred to as stacking dovetails) in the radially outer edge 66 of sector 58. FIG. 5B is a close-up front view of one of the dovetail slots 64 of FIG. 5A. The dovetail slots 64 of sectors 58 and the corresponding dovetails 62 of keybars 50 enable assembly and locking of sectors 58 onto respective keybars 50.
FIG. 6 shows three adjacent sectors 58 installed on respective keybars 50. Once attached to keybar 50, each lamination sector 58 is prevented from moving radially or tangentially. As seen in FIG. 6, each sector 58 is stacked only on one keybar 50 so as to suppress circulating currents within stator 30. Since stator or armature cores generally range from approximately 5 to 25 feet long, it is not practical to stack stator lamination sectors 58 onto the keybar dovetails 62 from the ends of keybars 50 because to do so would require each sector 58 to be slid a relatively long distance along the keybar dovetail 62.
To avoid such long sliding distances, one approach is to machine stacking slots 68 at regular intervals (for example, every 12 inches) along keybar dovetail 62 as shown in the bottom view of keybar 50 in FIG. 7A. In the end view of keybar 50 shown in FIG. 7B, one of stacking slots 68 is shown as a dashed line. In this manner, stacking slots 68 provide sectors 58 with access to keybar dovetail 62 at regular intervals. Sectors 58 are inserted on keybar dovetail 62 at a stacking slot 68 and are then slid a relatively short distance along dovetail 62 to the location of any previously installed sectors. This process is continued until the stator core is completely built up.
Thus, stacking slots 68 eliminate problems associated with sliding sectors 58 large distances along keybars 50 from the keybar ends. However, a typical large generator may include up to 21 or more keybars with lengths of up to 25 feet or more. Such dimensions would typically require the machining of approximately 400 to 500 stacking slots 68 in keybars 50. Unfortunately, the machining of such a large number of stacking slots adds significantly to the cost of a generator. Even with stacking slots, stacking the stator core with sectors 58 is a very time consuming process since much of the stacker's time is spent sliding sectors 58 down the keybar 50 from stacking slots 68. Moreover, the stacker must become proficient at taking a sector 58 and placing it at just the right location so that it will become engaged on the keybar dovetail 62 through stacking slots 68. Periodically throughout the stacking process, the stator core is compressed using hydraulic presses to tighten the stator lamination sectors 58 against each other. During this pressing operation, sectors 58 typically slide for several inches along keybar dovetail 62. If a lamination sector 58 becomes caught on a particular stacking slot 68 as it is being slid past such a stacking slot in the pressing process, a loose stator core may result.